In Figure 3.17, the three possible

In Figure 3.17, the three possible kinds of insertion of an instrument S (an active power or a reactive power meter) are illustrated.
The first (a in Figure 3.17) was described in the last subsection; if S is a wattmeter; the overall active power is given by three times its indication, and similarly for the reactive power if S is a reactive power meter.
Notice that a couple of twin resistors with the same resistance R of the voltage circuit of S are placed on the other phases to balance the load.